Your IP Address
How IP Detection Works
Your IP is detected server-side by PHP. The address shown is what your internet provider assigns to your connection.
- Public IP – Visible on the internet, assigned by your ISP.
- Private IP – Only reachable within your local network (RFC 1918).
- IPv4-mapped IPv6 – Server accepted IPv4 over an IPv6 socket (e.g.
::ffff:192.168.1.1). - Proxy headers –
X-Forwarded-For/X-Real-IPare set by load balancers or CDNs (e.g. Cloudflare) and may reveal your original IP.
IPv4 Subnet Calculator
How Subnetting Works
A subnet divides an IP network into smaller parts. The CIDR prefix (e.g. /24) tells you how many bits are used for the network — the rest are host bits.
- Network address – First address of the subnet (all host bits = 0).
- Broadcast address – Last address (all host bits = 1). Frames go to all hosts.
- Subnet mask – All network bits = 1 (e.g.
/24→255.255.255.0). - Wildcard mask – Inverse of the subnet mask. Used in ACLs and routing.
- Usable hosts – All addresses minus network and broadcast = 2ⁿ − 2.
IP Address Converter
IP Address Formats
- Dotted decimal –
192.168.1.1 - Hexadecimal –
0xC0A80101 - Decimal integer –
3232235777 - Binary – 32 bits in 4 octets
- IPv4-mapped IPv6 –
::ffff:192.168.1.1(RFC 4291) - 6to4 –
2002:c0a8:0101::/48(RFC 3056)
- Full (expanded) – all 8 groups, 4 hex each
- Compressed – leading zeros and
::omitted - Loopback –
::1 - IPv4-mapped –
::ffff:x.x.x.x - Decimal integer – 128-bit number
IPv6 ULA Generator
What is an IPv6 ULA?
Unique Local Addresses (ULA) are IPv6 addresses for use within private networks — the IPv6 equivalent of RFC 1918 private addresses (10.x.x.x, 192.168.x.x).
ULAs use the fd00::/8 prefix. The 40-bit Global ID is randomly generated to be statistically unique worldwide, so two networks can be merged without address conflicts — a big advantage over IPv4 private ranges.
RFC 4193 defines ULA. The usable prefix is fd00::/8 (the fc00::/8 half is reserved for future central allocation).
Generate a New ULA Prefix
ULA Structure & Usage Tips
| Bits | Field | Value |
|---|---|---|
| 7 | Prefix | 1111110 |
| 1 | L-bit | 1 (locally assigned) |
| 40 | Global ID | Random (crypto) |
| 16 | Subnet ID | Your choice (0–65535) |
| 64 | Interface ID | EUI-64 or random |
- Internal services that should never be reachable from the internet
- Lab or test environments
- Stable addresses independent of ISP assignment
- Merging two IPv6 networks (random Global IDs avoid conflicts)
Derived from the MAC address: insert FF:FE in the middle of the 48-bit MAC and flip bit 7. Example: 00:1A:2B:3C:4D:5E → 021a:2bff:fe3c:4d5e.
IP Range Calculator
Range → CIDRs
Enter a start and end IP address to get the minimal list of CIDR blocks that exactly cover the range.
CIDR → Range
Enter a CIDR block to see the full address range it covers including start, end, and host count.
About Range ↔ CIDR Conversion
Any arbitrary IP range can be expressed as a minimal set of CIDR blocks. The algorithm finds the largest aligned block that fits at the current start address, subtracts it, and repeats. A non-power-of-2 range will always require multiple CIDRs.
A CIDR block defines an exact power-of-2 range. A /24 always covers exactly 256 addresses. The network address is the first (all host bits = 0) and the broadcast is the last (all host bits = 1). Usable hosts = total − 2 (for /25 to /30).
IP Address Reference
IPv4 Special Address Ranges
| Range | CIDR | Hosts | Type | RFC |
|---|---|---|---|---|
10.0.0.0 – 10.255.255.255 | 10.0.0.0/8 | 16,777,214 | Private (Class A) | 1918 |
172.16.0.0 – 172.31.255.255 | 172.16.0.0/12 | 1,048,574 | Private (Class B) | 1918 |
192.168.0.0 – 192.168.255.255 | 192.168.0.0/16 | 65,534 | Private (Class C) | 1918 |
127.0.0.0 – 127.255.255.255 | 127.0.0.0/8 | – | Loopback | 5735 |
169.254.0.0 – 169.254.255.255 | 169.254.0.0/16 | 65,024 | Link-local (APIPA) | 3927 |
100.64.0.0 – 100.127.255.255 | 100.64.0.0/10 | 4,194,302 | Shared / CGN | 6598 |
192.0.0.0 – 192.0.0.255 | 192.0.0.0/24 | – | IETF Protocol | 6890 |
192.0.2.0 – 192.0.2.255 | 192.0.2.0/24 | – | Documentation (TEST-NET-1) | 5737 |
198.51.100.0 – 198.51.100.255 | 198.51.100.0/24 | – | Documentation (TEST-NET-2) | 5737 |
203.0.113.0 – 203.0.113.255 | 203.0.113.0/24 | – | Documentation (TEST-NET-3) | 5737 |
224.0.0.0 – 239.255.255.255 | 224.0.0.0/4 | – | Multicast | 5771 |
240.0.0.0 – 255.255.255.254 | 240.0.0.0/4 | – | Reserved | 1112 |
255.255.255.255 | 255.255.255.255/32 | – | Broadcast | 919 |
0.0.0.0 – 0.255.255.255 | 0.0.0.0/8 | – | This network | 1122 |
IPv6 Special Address Ranges
| Prefix | Description | RFC |
|---|---|---|
::1/128 | Loopback Equivalent to 127.0.0.1 | 4291 |
::/128 | Unspecified Equivalent to 0.0.0.0 | 4291 |
::ffff:0:0/96 | IPv4-mapped Embed IPv4 in IPv6 | 4291 |
64:ff9b::/96 | IPv4/IPv6 Translation NAT64 | 6052 |
fc00::/7 | ULA Unique Local (private), usable: fd00::/8 | 4193 |
fe80::/10 | Link-local Not routed, only on local segment | 4291 |
ff00::/8 | Multicast Replaced IPv4 broadcast | 4291 |
2000::/3 | Global Unicast Publicly routable addresses | 4291 |
2001:db8::/32 | Documentation For examples (like 192.0.2.0/24) | 3849 |
2002::/16 | 6to4 Automatic IPv4-compatible tunneling | 3056 |
100::/64 | Discard-Only Black hole routing | 6666 |
IPv4 Classful Network Classes
| Class | Range | Default Mask | Networks | Hosts/Net | Use |
|---|---|---|---|---|---|
| A | 1.0.0.0 – 126.255.255.255 | /8 | 126 | 16,777,214 | Large networks |
| B | 128.0.0.0 – 191.255.255.255 | /16 | 16,382 | 65,534 | Medium networks |
| C | 192.0.0.0 – 223.255.255.255 | /24 | 2,097,150 | 254 | Small networks |
| D | 224.0.0.0 – 239.255.255.255 | – | – | – | Multicast |
| E | 240.0.0.0 – 255.255.255.255 | – | – | – | Reserved / Experimental |
IPv4 CIDR Quick Reference
| CIDR | Subnet Mask | Hosts | Subnets of /24 | Notes |
|---|
Key Concepts
IPv4 vs IPv6
IPv4 uses 32-bit addresses (≈4.3 billion). IPv6 uses 128-bit addresses (≈340 undecillion) to solve IPv4 exhaustion. IPv6 has no broadcast — multicast replaces it.
CIDR (Classless Inter-Domain Routing)
Replaced classful networking. A /24 means 24 bits for the network, 8 for hosts. CIDR enables efficient IP allocation and route aggregation (supernetting).
NAT (Network Address Translation)
Allows multiple devices with private IPs to share one public IP. Common in home routers. IPv6 makes NAT unnecessary — every device can have a globally unique address.
Subnet Mask vs Wildcard Mask
Subnet mask: 1s mark network bits (255.255.255.0). Wildcard: 0s mark network bits (0.0.0.255). Wildcards are used in Cisco ACLs and OSPF.
VLSM (Variable Length Subnet Masking)
Lets you use different subnet sizes within the same network. E.g. a /30 for point-to-point links (2 hosts) and a /24 for offices (254 hosts).
IPv6 Prefix Delegation (PD)
ISPs assign a /48 or /56 to customers. The customer splits it into /64 subnets — one per LAN segment. Each /64 supports 2⁶⁴ addresses.